Our goal is to test whether DEAD-END (DND1) can counteract the effect of increased miRNA expression in cancers in mice. DND1 has RNA recognition motifs through which it binds to mRNAs to block miRNA access to mRNAs. miRNA-mRNA interaction generally results in translational repression or degradation of mRNAs and the consequence is reduced protein expression. DND1 prevents miRNA-mRNA interaction and can override the presence of miRNAs to restore protein expression. However, this function of DND1 has only been demonstrated in cell lines in culture. Therefore, our goal is to test the miRNA blocking function of DND1 in vivo. Specifically, we will test whether DND1 is able to counteract the oncogenic effect of higher miRNA levels in mouse models of pancreatic cancers. We are currently generating transgenic mice that will conditionally express DND1 in any cell type. This will allow us to express DND1 in the pancreas of KRASG12D-mutant mice. KRASG12D-mutant mice develop pancreatic intraepithelial neoplasias (PanINs) that overexpress miR-221. We will determine if DND1 counteracts the effects of miR-221 to reduce PanIN development. miR-221 decreases protein expression of the cell cycle inhibitor P27. We will determine whether DND1 restores P27 expression in the pancreas of KRASG12D-mutant mice. Second, we will test whether DND1 deficiency has the opposite effect of increasing PanIN development in KRASG12D-mutant mice. Together with the genetic studies, we will test tumorigenicity of KRASG12V-transformed human pancreatic cancer cells that express ectopic DND1. Further, we will examine whether the physiological effects of increasing DND1 in human and mouse cells is because of stabilized expression of cell cycle inhibitors such as P27. We will determine whether increasing DND1 levels quantitatively correlate with greater interaction of DND1 with P27 mRNA, higher P27 expression, decreased cell proliferation and tumorigenesis. The proposed studies represent the first proof of principle study to test the possibility of using DND1-like factors to counteract miRNA-mediated oncogenesis in vivo. These studies could identify a novel strategy to block miRNA function in vivo and a possible future therapeutic use of DND1 in human cancers.